In all likelihood, the fish are basically starving.
At 28C, they start exogenous feeding at 5 days, but also continue to derive nutritional benefit from the yolk sac, but this is generally gone by day 7. If you don't give them any food at all, they will starve at day 10 or so.
No matter how dense, standard, bacteria-fed Paramecium does not meet the considerable nutritional demands of the fish beyond the first few days of feeding. If you do not present the larvae with something else with a better nutritional profile (higher protein, and specific lipid content) at this point, they will starve. If all of your fish die by 12-14 days, then that is likely what is happening. The Paramecium typically gets them out a day or two longer than the 10 day mark. Even if you manage to keep them alive beyond that, they won't grow until you give them something with an adequate nutritional profile. You're just prolonging the starvation.
If you start feeding Paramecium at day 5 (as soon as they are swimming), you should be presenting them with another item, in small, frequent applications, whether it be first stage Artemia nauplii or a processed larval feed, by 7-9 days. Once you begin do this, you should put them on flow at a slow drip to maintain stable (but not necessarily pristine) water quality. Once it becomes apparent that they are feeding on the new items (full guts, rapid growth), you can stop the paramecium applications, increase the amounts of the new feed per feeding, and slowly increase flow rates as the fish grow.
The weaning from a low nutritional quality first feed like Paramecium to something better is the key to success in larval rearing. If you don't do it correctly or well, your survival rates will always be poor.
Chris
On 9/7/09 12:11 AM, "chubbyjayu" <chubbyjayu from gmail.com> wrote:
Hello all!
I have been trying to raise zebrafish larvae in the lab
unsuccessfully. The problem is that the larvae tend to die 12 - 14
days post fertilization and there seems to be no logical cause for the
death.
I check the paramecium stocks for coleps everyday, but see none. We
have even tried raising the zebrafish larvae in embryo medium (made
as per the zebrafish book), but even then we see that the larvae die
out within 14 days.
Could you please help me figure out where I am going wrong?
Jayasree
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